1. Field of the Invention
The present invention relates to an inkjet printing apparatus that performs printing by ejecting ink onto a printing medium, such as a printing sheet, and an inkjet printing system and an inkjet printing method therefor.
2. Description of the Related Art
With respect to the production of elongated print heads for use in full line-type inkjet printing apparatuses, many problems exist that affect both the technique employed and the costs involved in the high density arrangement, in a line, of multiple nozzles on a single substrate. Therefore, a chip joining type print head (hereinafter also referred to as a “multi-segment print head”) is employed in line-type inkjet printing apparatuses. The multi-segment print head is an elongated print head provided by arranging, in a zigzag manner, a plurality of comparatively short heads (hereinafter also referred to as “chips”), in each of which multiple nozzles are closely arranged.
For arranging multiple chips, accurate positioning is required. If precise positioning fails, and chips are offset from adjacent chips, a white line or a black line (hereinafter also referred to as a joint defective line) may appear at the image portion corresponding to the joint between the adjacent chips, deteriorating the printing quality. Further, if the print head is not accurately mounted at the head position of the ink-jet printing apparatus, this line-like printing defect will also appear.
A method for suppressing such printing defects is proposed in Japanese Patent Laid-Open No. H05-57965 (1993). According to this method, multiple chips are arranged so they overlap the ends of adjacent chips, and in the overlapping portion of one chip, the print density of dot (printing duty) is gradually reduced, while in the overlapping portion of the other chip, to complement the print density reduction, the print density is gradually increased.
However, as in the case of Japanese Patent Laid-Open No. H05-57965 (1993), wherein the print densities in overlapped portions of adjacent chips are complementarily increased and decreased, when a misalignment of relative chip positions occurs, the complementary print density relationship is not maintained for the overlapping portions of the adjacent chips, and density fluctuation occur. Methods for resolving the offset of chip positions, such as by shifting image data, or shifting the area covered by a nozzle so as to shift the print positions of chips, are well known. However, these methods for adjusting print positions can not be carried out without either the shifting of image data for each pixel, or the shifting of nozzle coverage area for every nozzle pitch. Because of this, when chips are misaligned, for example, a distance equivalent to half the size of a pixel, the density fluctuation caused by this offset cannot be reduced by these methods.